Axial flow compressor regulation



Oct. 7, 1952 c. L. WILDE ,0

AXIAL. mow COMPRESSOR REGULATION File d June 1, 1948 2 SHEETS-SHEET 1WAC/W01? 6% 1. WM 05 K/MaMzz-W Oct. 7, 1952 G, 1.. WILDE 2,613,029

AXIAL FLOW COMPRESSOR REdULIATION Filed June 1, 1948 2 SHEETS-SHEET 2Patented Oct. 7, 1952 AXIAL FLOW COMPRESSOR REGULATION Geoffrey LightWilde, Coxbench, England, as- Signor to Rolls-Royce Limited, Derby,England,

a British company Application June l, 1948, Serial No. 30,330 In GreatBritain June 4, 1947 This invention relates to, multi-stage axial flowcompressors and has for its object to provide such a compressor with awide speed-range of operation.

It is usual to design such a compressor to run etliciently at aparticular rotational speed or at a condition dependent on rotationalspeed, and this involve designing the blades, so that all the stages canbe ideally matched to give a selected, for instance constant, axialvelocity of the fluid to be compressed, from entry to exit at theparticular rotational speed or condition dependent on rotational speed.

The term rotational speed covers either the actual rotational speed ofthe compressor or the corrected rotational speed of the compressor 1. e.the actual rotational speed divided by the square root of the absolutetemperature at the inlet to the compressor, since, as is well known inthe art, a compresso may be designed to operate ciliciently at aselected value of the actual rotational speed or of the correctedrotational speed or of a condition dependent on either one of these twospeeds.

The angle of incidence at which the rotorblades operate, for any givenspeed of rotation, is determined by the axial velocity of the fluid andthe direction of swirl given to it by the stator At rotational speedsbelow the designed speed, when the pressure rise per stage is less thanthe designed pressure-rise, there will tend to be an accelerating flowfrom entry to exit due to the designed overall density-ratio not beingachieved. This acceleration appearsas a reduction of the axial velocityof the fluid at the entry and an increase at the exit.

Where the axial velocity of the fluid is lower than the designed axialvelocity, the angle of incidence becomes positive and so high that theblades run in a stalled condition, and where the axial velocity ishigher, the blades run at a negative angle of incidence and therefore donot contribute their share of the stage pressure-rise.

At rotational speeds above the designed speed, when the pressure-riseper stage is greater than the designed pressure-rise, there will tend tobe a decelerating flow from entry to exit due to the design overalldensity-ratio being exceeded; this deceleration appears as an increaseof the axial velocity at entry and a decrease at exit. These conditionsare therefore opposite to what occurs when the rotational speed isbelowthe designed speed as described above.

The object of this invention is to provide for adjusting the rotationalswirl oi the fluid to suit uoiaims. (01. 230-414) 2 any variations inthe axial velocity of the iluid which arisefrom changes in the speed ofthe rotor from the designed speed. i

The primary object of the present invention is to provide a constructionof multirstage axial flow compressor in which the flow conditions arecontrolled in such a manneras to maintain a high efficiency ofcompression throughout a wide range of rotational speed.

According to the present invention, a multi stage axial-flow compressoris arranged in a plurality of sections each comprising a plurality ofstages, and is provided with a row of adjustablepitch stator-blades atthe entry to each section to vary the rotational swirl of the fluidleaving them and entering the section, and 50 to avoid the diffi'cultiesmentioned above and provide a multistage axial-fiow compressor having awid speedrange of operation and good efficiency at low speeds and atstarting. According to a feature of the invention, the means foradjusting the pitch of the adjustablepitch stator blades may beconnected with a devicesensitive tothe speed of thecompressor, so thatthe pitch of the blades is adjusted to a predetermined setting for anycompressor-speed other than the designed speed.

According to another feature of this invention, the means for adjustingthe pitch or the adjustable-pitch stator blades may be connectedwith adevice sensitive to an operating variable which varies as a uniquefunction of rotational speed. Thus in some constructions according tothe invention the means for adjusting the pitch of the adjustable pitchstator blades may be connected with a device sensitive to th ratiobetween the inlet and discharge pressures of the compressor,

since this ratio varies as a unique function of corrected rotationalspeed. I

Some embodiments of the invention will, now

' be described by way of example, reference being made to theaccompanying drawings in'which,

Figurel is a diagrammatic plan of a multistage axial compressor andmeans for varying the pitch of the adjustable stator blades,

Figure 2 is a side elevation of part of the compressor with partsinsection to show the manner in which the adjustable stator blades aresupported, I 1

Figure 3 is a scrap view showing means for adjusting the pitch of onerow of stator blades,

Figure 4. is a diagrammatic section on the line 4--4 of Figure 2illustrating the manner of pitch adjustment of the entry stator bladesof one tion of the compressor; f

' Figure 5 is a corresponding view on the line ing from the inlet l3 ofthe compressor to the.

outlet therefrom. The rotor lllb is driven through a shaft l4 which inaircraft gas-turbine engines usually extends between thecompressor rotorand a turbine rotor.

The compressor is divided into a number of sections each comprising aplurality of stages, each stage comprising a row of stator blades II anda row of rotor blades l2, and the entry row of stator blades ofeach'section areadjustable in pitch for the purpose above described.Thus in the construction illustrated, the compressor is divided into lowpressure and high pressure sections of which the first-stage statorblades Ila are the adjustable entry blades for the low pressure sectionand the seventh stage stator blades llb are the adjustable entry bladesof the high pressure section.

Each blade Ila is formed at each end with a trunnion I5, the outertrunnion engaging in a bearing in the compressor casing Wu and the innertrunnion being engaged in a bearing in a stationary annular frontbearing housing l6 supported within the casing Illa by the inlet guidevanes II. Each of the inner trunnions l has a pin-like extension I8projecting within the housing I6 and having secured on it a rocker arml9. Each rocker arm has an upstanding pin at its end to engage with anotch in a ring 2l. The ring 2| is rotatively mounted in the housing l6and is internally notched, there being one notchfor each pin 20 and thusfor each of the stator blades Ila. Thus it will be seen that if the ring2I is rotated, the arms I9 will be rocked and the blades lla rotatedabout their lengthwise axes to adjust their pitch.

The following arrangement is adopted to rotate the internally-notchedring 2I. The outer trunnion l5 of one of the blades Ila/has a squaredextension 22 projecting outside the compressor casing Illa and thisextension has secured on it alever 23 connected by a link to the ram 25of a hydraulic jack 26. Telescoping of the jack 26 will rock the lever23 to rotate the blade Ila carrying it and this rotation will betransmitted to the ring 2| through the associated arm l9.

Each blade llb is mounted to rotate about its lengthwise axis by beingsupported in the casing Illa. through a trunnion 2'! on its outer end.Each trunnionZl has secured to it an arm 28 which engages by its freeend in an internallynotched ring '29 rotatlvely mounted inv aninternally-recessed flange 30 on the casing Ifla. One of the arms 28 hasa rearward extension 3| which is connected by a link 32 to the ram 33 ofa hydraulic jack 34. Telescoping of the jack 34 will rock the lever 28,3| causing the. ring 29 to rotate relative to the casing llla, therebyrocking the remaining arms 28 .and causing the blades. llb torotateabout their lengthwise axes to adjust their pitch.

Referring more particularly to Figures 1, 4 and 5, the means forcontrolling the pitch is such that if the compressor speed is below apreselected speed the pitch of the blades Ila and Ilb is adjusted by thejacks 26, 34 respectively to occupy the chain-line positions indicatedwhile for normal running at above the preselected speed the bladesoccupy the full-line position. The direction of rotation of the rotor isindicated by arrow 35.

The control means comprises a centrifugal de vice 36 driven by anysuitable drive 37 from the shaft I4. The centrifugal device produces aforce which is a functionof compressor speed and this force is opposedby the spring I36. The centrifugal device carries a contact arm 38 andit is arranged that when the preselected compressor speed'is reached anelectrical circuit 39 is completed by the contact on arm 38 engaging afixed contact 40 thereby energising a solenoid 4|. The solenoid controlsa piston valve 42 controlling the flow of liquid through a hydrauliccircuit between a pump 43 and the jacks 25, 34. The pump 43 draws liquidfromthe reservoir 44 and when the solenoid ll is energised the pressurefluid is delivered to the jacks through pipes 45 holding the. levers 23,3| in their full-line position (Figure 1) which corresponds to thefull-line positions of the blades Ila, I lb (Figures 4 and 5), whilstwhen the solenoid is de-energised the pipes 46 leading to the oppositeends of the jacks 2t, 34 are connected to the pressure fluid and thelevers 23, 3I occupy their chain line positions. A spring 41 is providedto urge the piston valve :32 to the right as viewed in the drawings ondeenergization of the solenoid M.

.It will be seen that at speeds below the pre selected. speed, the inletblades II a are adjusted to. increase the swirl caused by them in thedirec tion of rotation 35 of the rotor blades l2, whilst the inletblades llb to the second section are adjustedto. a position in which theswirl they cause in the direction of rotation of the rotor blades I2 isdescribed.

This arrangement ensures that stalling of the compressor at lowrotational speeds does not occur.-

The preselected speed at which adjustment of the blades Ila, llb occurscorresponds to a given ratio between the pressures at the compressorinlet l3 and at the compressor outlet and this fact is employed in analternative controller to the centrifugal device 36 and spring I36.

Referring to Figure 6, the alternative controller. comprises twopressure sensitive capsules, one 50 of which. is enclosed in a chamber5| connected to thecompressor inlet and the other of which is enclosedin a chamber 53 connected to the compressor delivery. The capsulesoperate on a pivoted beam-54, the pivot 55 for which is closer tothe-end of the beam connected to capsule 52 than to the other end.Assuming that the. capsules are ofequal effective area,then the beamwill be rocked to close the circuit 39 by contact as engaging fixedcontact 40, when the ratio of the outlet pressure-to inlet pressureexceeds the. ratio of the longer beam arm to the shorter beam armandthis'occurs at a predetermined speed. of thecompressor. 40, 56.controlsadjustment of the pitch of blades Ila, llli in-the mannerdescribed with reference toFigures 1., 4 and 5.

The invention. is-not limited to the constructions. above described. Thecompressor may be divided into more than two sections having the firstrow of stator blades adjustable in pitch; the higher the designedrunning speed and pressure Closing of the contacts ratio of thecompressor, thegreater is the change in pitch required to improve'efiiciency at low speeds. For instance a compressor designed to run at ahighspeed may have adjustable rows of stator blades at the inlet stage,the second stage, seventh stage and tenth stage,the first two beingincreased in pitch at low speedandthe two latter decreased inpitch,

Furthermore, instead of providing only two positions for the statorbladesthey may be made to occupy more than two positions or to becontrolled by a follow-up mechanism between the governor and blades sothat their pitch is varied section, each section comprising 'a pluralityof stages, said compressor further comprising a stator casing; a row ofstator blades at'the entry to each said section; bearing meanssupporting the stator blades of each said row in said casing so as to beadjustable inpitchgqmotor means operative to rotate each row of statorblades in unison but in opposite directions; a power supply for saidmotor means; andpower supply "control means, including a devicesensitive to the speed of the compressor, automatically "to control thepower to supply to said motor means to rotate the stator blades of saidlow pressure, section to give an increased swirl in the direction ofrotation of the compressor at low compressor speeds and to rotate thestator blades of said high pressure section to give a decreased swirl atlow compressor speeds.

2. In a multi-stage axial-flow compressor, of the class having aplurality of rows of stator blades adjustable in pitch, the combinationwith each of said rows of a jack to adjust in pitch in unison all theblades in the row from a first posi-.

tion to a second position, a source of fluid pressure, fluid connectionbetween said source and said jack, a two-position control valveoperative in its first position to. connect one end=of said jack withsaid source, and in its second position to connect the other end of saidjack to said source, a loading device biasing said valve to one of saidpositions, a solenoid operative whenenergised to move said valve againstsaid loading device to its other position, a source of electric power,an electric switch, electric connections connecting said solenoid, saidsource of electric power, and said switch in an electric circuit inseries, and speed-sensitive means arranged to be sensitive to therotational speed of said compressor and operative alternately to openand close said switch when said rotational speed passes through aselected value.

3. A combination according to claim 2, wherein a single source of fluidpressure and a single control valve are common to all the jacks. J

4. In a multi-stage axial-flow compressor of the class having aplurality of rows of stator blades adjustable in pitch, the combinationwith each of said rows of a jack to adjust in pitch in unison all theblades in the row from a first position to a second position, a sourceof fluid pressure, fluid connection between said source and said jack, atwo-position control valve operative in its first position to connectone end of said jack with said source and in its second position toconnect the other end of said jack to said source, a loading devicebiasing said valve to one of said positions, a solenoid operative whenen 6, ergised to move said valve against saidloading device to its otherposition, a source 'of electric power, an electric switch, electricconnections connecting said solenoid, said source of electric power andsaid-switch in an electric circuit in series, and pressure-sensitivemeans sensitive to the ratio between the pressures from the inlet to theoutlet of said compressor and operative alternately to open and closesaid switch when said ratio passes through a selected value.

' 5. A combination according to claim 4, wherein a single source offluid pressure and a single control valve are common to all the jacks.

6. A multi-stage axial-flow compressor comprising a high pressuresection and a low pressure section, each section comprising a pluralityof stages," said 'compressoriurther comprising a stator casing, a row ofstator blades at the entry to each said section, bearing meanssupporting the stator blades of each said row in said casing so thatthey are adjustable in pitch, flrstmotor means to rotate the statorblades of the row at entry to'the high pressure section, second motormeans operative to rotate the stator blades of the row atentry to thelow pressure section, a power supply for; said motor means,speed-sensitive mean'ssensitive to the compressor rotational speed, andservo means operated by said speedsensitive meansto place said powersupply in connection with said first motor means to rotate said row ofstator blades at entry to the low pressure section in thedirectiontoincrease their outlet angle relative to the axial directionand to place said power supply in connection with said second motormeans to'rotate said row of stator blades at the entry to the highpressure section in the directionto decrease their outlet angle relativeto the axial direction, until the pitch of the blades of the two rows isadjusted in opposite senses to 'apredetermined setting depending onthespeed of the compressor.

'7. A multi-stage axial-flow compressor comprising a plurality'ofsections, each section comprising a plurality of stages, said compressorfurther comprising a stator casing, a rowof stator blades at the entryto each said section, bearing means supporting the stator blades of eachrow in said casing so thatthey are adjustable'inpitch, jack devicesoperative to rotate the stator blades of each row in unison, a supply ofpressure fluid for said jack devices, a centrifugal device to produce aforce which is a function of compressor rotational speed and increaseswith increase of said speed, means to oppose said force, an electriccircuit arranged to be completed by said centrifugal device onovercoming said opposing force due to sensing a preselected speed ofsaid compressor, a solenoid arranged to be energized on completion ofsaid electric circuit, valve means arranged to be moved between twopositions by said solenoid device, conduit means from said pressurefluid supply to said valve means and conduit means from said valve meansto said jack devices to deliver pressure fluid to one end thereof whensaid valve is in one position and to deliver pressure fluid to the otherend thereof when said valve is in the other position whereby the supplyof pressure fluid to said jack devices is controlled when saidrotational speed passes through said preselected speed to rotate thestator blades of said rows until the pitch of the blades of each row isadjusted to a predetermined pitch depending on said rotational speed.

8- A multi-stage axialrflow compressor comprisinga plurality ofsections; each. section comprising a plurality of stages, said.compressor further comprising a stator casing, a row of stator bladesatv the entryto each said section, bearing means supporting the statorblades of each row in said casing so that they are adjustable in pitch,motor means operative to rotate the stator blades of each row in unison,a power supply forsaid motor means, pressureratio-sensitive meanscomprisinga pair of resilient pressure-sensitive capsules. connectedre.- spectively to an inlet pressure and an outlet pressure of. thecompressor, :and a pivoted beam arranged to be loaded. in-opposition bysaid capsules, an electric circuit-arranged to be completed when apredetermined pressure ratio is sensed by said pressure-ratio-sensitivemeans and servo means operated oncompletion of said electric circuit toplace said power .supply in connection withsaid motor means .to' rotatethe stator blades of said rows until the pitch of-the blades of each rowis adjusted toa predetermined setting dependent on the speed of thecompressor.

9. A multi-stage axialflow compressor com-v prising a, pluralityofsections, each. section comprising a plurality of stages, saidcompressor further comprising a stator casing, a row of stator blades atthe entry of each section, bearing means supporting the statorbladesofeach row in said casing so that they are adjustable in pitch, motormeans to rotate each row of: said stator blades, means controlling saidmotor means to cause said rows of blades to rotate. in unison but inopposite directions, and speed-sensitive means sensitive,

to the compressor rotational speed to operate said motor controllingmeans until the pitch of the blades is adjusted to a predeterminedsetting depending on the speed of the compressor.

10. Amulti-stage axial-flow compressor com.- prising aplurality ofsections. each section comprising a plurality of stages, said compressorfur ther comprising a stator casing, arow of stator blades at the entryto. each said-section, bearing means supporting the stator blades ofeach. row in said casing so that they arev adjustable. in pitch, motormeans torotate each row of said stator blades, means controlling saidmotor means to cause said rows of blades to rotate in unison'but inopposite directions, and a sentrifugal device-driven by the compressorto producea force which isa function of compressor rotational'speedand:.increases with increase of speed, aspring to oppose said force,said motor controlling-means being operated when said force produced bythe centrifugal device overcomes said spring so that the stator bladesof said rows are rotateduntil the pitch of the blades of each row isadjusted to a predetermined setting depending on the speed of thecompressor.

11. A multi-stage axial flow compressor comprising a power input shaftsubject to variable driven speeds of rotation, a high pressure sectionand a low pressure section both driven by said shaft, each sectioncomprising a plurality of stages, said compressor further comprising astator casing; a row of stator blades at the entry to each said.section; bearing means supporting the stator blades of each said row insaid casing so as. to be adjustable in pitch; motor means operative torotate each row of stator blades in unison but in opposite directions; apower supply for said motor means; and power supply control means,including a device sensitive to the speed of the compressor,automatically to control the power supply to said motor means to rotatethe stator blades of said low pressure section to give an increasedswirl in the direction of. rotation of the compressor at lowcompressorspeeds and to rotate the stator blades of said high pressuresection to give a decreased swiral at low compressor speeds.

GEOFFREY LIGHT WILDE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,010,555 Moody Aug. 6, 19352,361,007 Buchanan Oct. 24, 1944 2,361,887 Traupel Oct. 31, 19442,371,706 Planiol -1 Mar. 20, 1945 2,409,836 Coe Oct. 22, 1946 2,409,837Alford Oct. 22, 1946 2,435,092 Meyer Jan. 27, 1948 2,500,070 Hagen Mar.7, 1950

